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Caption

Castor oil plant seed. Light micrograph of a section through the seed of a castor oil plant (Ricinus communis). The castor oil seed has an outer testa (not seen) which is poisonous. Under the testa is the endosperm storage tissue (blue), which provides nutrition for germination. The cells of the endosperm are full of aleurone (protein) grains. The embryo, in the centre of the seed, consists of two cotyledons. Magnification: x3.5 when printed 10 centimetres wide.